This invention relates to antenna tuning, particularly but not exclusively to tuning a patch antenna using a switch.
Patch antennas are well-known and are well-suited for use as internal antennas in mobile telephones, since they can be made relatively small.
The problem with patch antennas is the need to trade-off size and bandwidth, since, in general, the smaller the antenna, the smaller its bandwidth. Since antennas need to be small to fit within modern mobile telephones, a solution is required to the problem of providing sufficient bandwidth for effective operation, including operation across multiple bands. There are two possible approaches to solving this problem, the first being to use multiple antennas and the second being to use a variable tuning scheme, so that the antenna can be made to cover different frequency bands.
In accordance with the invention, there is provided a tunable antenna for a portable communications device, comprising an antenna arrangement comprising first and second spaced apart conductors, the first conductor comprising a radiating conductor and the second conductor comprising a ground plane, the radiating conductor including first and second feed points arranged such that a resonant frequency of the antenna arrangement when fed at the first feed point is different from a resonant frequency of the antenna arrangement when fed at the second feed point, further comprising a switch for switching between the first and second feed points.
According to the invention, there is further provided a tunable antenna for a portable communications device, comprising an antenna arrangement connectable to an antenna feed, the antenna arrangement comprising first and second spaced apart conductors, the first conductor comprising a radiating conductor and the second conductor comprising a ground plane, the radiating conductor including first and second feed points; and a capacitor having first and second terminals, said first terminal of said capacitor being connected to said first feed point, further comprising a switch arranged to selectively switch the antenna feed between said second terminal of said capacitor and said second feed point.
The invention further provides a method of tuning an antenna for a portable communications device, the antenna comprising first and second spaced apart conductors, the first conductor comprising a radiating conductor and the second conductor comprising a ground plane, the radiating conductor including first and second feed points arranged such that a resonant frequency of the antenna arrangement when fed at the first feed point is different from a resonant frequency of the antenna arrangement when fed at the second feed point, the method including switching an antenna feed between the first and second feed points.